STUDY ON LOCAL DELAMINATED THERMAL BUCKLING OF COMPOSITE LAMINATED PLATES

Based on the Whitcomb delaminated buckling model, a Rayleigh-Ritz analysis is presented to study the local thermal buckling problem of elliptical, rectangular, triangular, and lemniscate delaminations in a symmetric composite laminated plate. The critical temperatures of the laminated plate with various shaped local delaminations and different stacking patterns are obtained by utilizing the energy principle. The geometrical axis of various shapes of local delamination is arbitrary. The stacking sequence of base laminated plates is symmetric, but the stacking sequence of the sublayer is asymmetric. Finally, our experimental study on the mechanism of delaminated buckling failure in a laminated plate with a single elliptical and rectangular delamination near the surface of the laminated plate under thermal load was accomplished. Analytical predictions for the critical temperature yielding the local delamination buckling are shown to correlate well with experimental results for a number of different delamination shapes.     

REFINED HIGHER ORDER FINITE ELEMENT MODELS FOR THERMAL BUCKLING OF LAMINATED COMPOSITE AND SANDWICH PLATES

Two refined higher order theories, one that neglects and the other that takes into account the effect of transverse normal deformation, are used to develop two discrete finite element models for the thermal buckling analysis of composite laminates and sandwiches. The two models, one with nine degrees of freedom per node and the other with eleven degrees of freedom, are based on a nine-node Lagrangian isoparametric element. The geometric stiffness matrices are developed by taking into consideration the effects of the higher order terms on the initial in-plane and transverse shear stresses. The accuracy of the present formulations is first evaluated by analyzing sample problems for which analytical three-dimensional solutions exist in the literature. Numerical results are presented for the first time for sandwich plates, demonstrating the importance and accuracy of the higher order theory in comparison to first-order theory. Some new results are also given for sandwich plates with angle-ply composite face sheets, showing the effects of various boundary conditions and of variations in geometric and lamina tion parameters on critical temperature.     

BUCKLING BEHAVIOR OF LONG ANISOTROPIC PLATES SUBJECTED TO RESTRAINED THERMAL EXPANSION AND MECHANICAL LOADS

An approach for synthesizing buckling results and behavior for thin balanced and unbalanced symmetric laminates that are subjected to nondestabilizing mechanical preloads, uniform heating or cooling, and elastically or totally restrained axial thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined loads and is based on useful nondimensional parameters. In addition, a stiffness-weighted laminate coefficient of thermal expansion is derived and used to determine critical temperatures in terms of physically intuitive mechanical buckling coefficients, and the effects of membrane orthotropy and membrane anisotropy are included. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented in the article. Several generic buckling design curves are presented that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of the generic design curves. The analysis approach and generic results identify the effects and characteristics of laminate thermal expansion, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.     

FLEXURAL CHARACTERISTICS AND LAYUP OPTIMIZATION OF LAMINATED COMPOSITE PLATES UNDER HYGROTHERMAL CONDITIONS USING LAMINATION PARAMETERS

The flexural characteristics and layup optimization of laminated composite plates are examined in environmental conditions of temperature and moisture. The deflection of laminated composite plates is analyzed in the design space of 12 lamination parameters. The layup optimization for minimizing the deflection of laminated composite plates is carried out using all 12 lamination parameters as design variables. Mathematical programming methods are used for optimization. In hygrothermal conditions, the maximum deflection of laminated composite plates with in-plane hygrothermal stresses can be reduced by optimized nonsymmetric laminate configurations.     

海水换热器析晶污垢物相分析及动力学研究

海水换热器常用于沿海能源和化工领域的海水直流冷却系统和循环冷却系统。海水在热交换的过程中容易产生析晶结垢,造成换热效率下降和管路堵塞,这些污垢的组成及结垢机理是目前研究热点之一。本研究搭建一套海水结垢的可视化实验装置,对海水在换热过程中形成的析晶污垢进行了物相分析和动力学研究。通过X射线衍射(X-ray Diffraction,XRD)、扫描电镜(Scanning Electron Microscope,SEM)和X射线能谱(Energy Dispersive X-Ray,EDX)分析海水换热器析晶污垢的元素组成和晶体结构,结果显示污垢的元素组成和晶体结构与水合氢氧化镁铝(Mg_6Al_2(OH)_(18)·4.5H_2O)十分相似。基于Kern-Seaton模型,建立适用于海水析晶污垢的动力学模型,并根据实验结果对结垢过程的动力学参数进行拟合。结果表明:在不锈钢表面海水析晶结垢的表观活化能为1.54×10~4J/mol,在实验工况下海水析晶结垢是一种扩散控制过程。     

MODELS AND TOOLS FOR HEAT TRANSFER,THERMAL STRESSES,AND STABILITY OF COMPOSITE AEROSPACE STRUCTURES

An overview of DLR's current research activities and results in the fields of heat transfer, thermal stresses, and thermally induced buckling in composite aerospace structures is given. Novel theories and finite element formulations are presented, realistic modeling of boundary conditions and junction areas is highlighted, experimental validation is discussed, and design guidelines are given.     

海上风电场功率提升和疲劳平衡综合优化控制

针对海上风电场,综合功率提升和疲劳平衡分配的优化目标,提出一种以天为优化周期的优化策略.在电网高负荷时段,基于Jensen尾流模型,以轴向诱导因子为优化变量,风电场整场功率最大为目标,运用随机粒子群算法进行风功率利用提升优化控制;在电网低负荷时段,基于风电机组综合疲劳系数计算方法,以机组轴向诱导因子为优化变量,应用尾流...     

适合于太阳能热发电的锰铁锂复合金属氧化物储热特性与热化学反应机理

提出在锰基氧化物中添加Fe₂0₃和Li₂0,构建锰铁锂三元复合金属氧化物,降低热化学储热反应温度,更好地满足新一代太阳能热发电系统需求。实验发现,与Mn₂O₃相比,新生成的Li₂FeMn₃O₈复合氧化物的还原反应初始温度由773℃降低至622℃;还原反应活化能从797.10 kJ/mol降低至132.44kJ/mol;氧化反应由难以进行,变为从590℃开始进行;氧化放热量增至209.40 kJ/kg;经过105次循环后仍保持良好的循环反应稳定性。     

小型风力发电系统最大功率控制扰动法及状态平均建模与分析

为简化结构、降低成本、提高可靠性及实现系统优化运行,提出了包含永磁同步发电机、二极管整流桥及斩波器的小型风力发电系统结构,采用扰动法来实现最大功率控制,利用状态平均法对系统进行建模,导出了相应的静态特性及线性化模型,给出了扰动幅值及频率这两个关键参数的选取原则,通过实验验证了控制策略及分析方法的正确性和可行性。为最大功率控制扰动法在小型风力发电系统中的应用提供了理论依据,具有重要的理论意义及实际应用价值。     

塔式太阳能熔盐吸热器运行特性与策略优化

该文研究太阳光照条件、环境温度、风速、风向等因素对塔式太阳能热发电熔盐吸热器整体热效率和散热损失的影响规律,讨论吸热器的运行策略及其对系统效率的影响.吸热器的运行受风速和入射能量的影响较大,受风向和环境温度的影响较小.额定出口温度模式下,当风速超过7m/s时,对流散热损失超过辐射散热损失.风速对吸热器局部对流散热损失的...     

中国不同气候区日总太阳辐射计算模型适用性分析及通用计算模型优化

利用中国5个气候区96个气象台站的1981—2010年的日值气象数据,对比分析12个基于日照百分率和12个基于温度的日总太阳辐射计算模型在不同气候区的适用性。采用判定系数（R²）、均方根误差（RMSE）、平均绝对误差（MABE）、平均误差（MBE）和全局性能系数（GPI）5个评价指标,确定各气候区最适宜的模型形式。以该模型为基准,建立适用于中国不同气候区的基于日照百分率和基于温度的日总太阳辐射通用计算模型。结果表明,三次方形式的基于日照百分率和基于日较差-平均温度的模型在各气候区计算精度均最高;以该模型为基础,建立适用于中国不同气候区的基于日照百分率和基于温度的日总太阳辐射通用计算模型,其平均R²分别为0.91和0.68。